1. Field of the Invention
The present invention relates to a motor with dynamic pressure bearing that is equipped with a dynamic pressure bearing member that supports a rotary shaft by utilizing dynamic pressure generated in a lubricating fluid.
2. Related Background Art
In recent years, development of dynamic pressure bearing motors, in which a dynamic pressure bearing member or dynamic pressure bearing sleeve supports a rotary shaft by utilizing dynamic pressure generated in lubricating fluid, has been in progress for bearing apparatuses that allow rotating bodies to rotate at high-speed and with high precision to be used in various rotatively driven apparatuses. An effort is underway to make the entire apparatus thinner for such dynamic pressure bearing motors, and forming a thrust bearing section by utilizing an end surface in the axial direction of a dynamic pressure bearing sleeve has been proposed in order to achieve such thinner apparatus.
In such dynamic pressure bearing motors, a dynamic pressure bearing sleeve is inserted through and fixed to the inner side of a generally cylindrical holder member that holds a stator core, and a rotary hub is mounted on a rotary shaft that is supported in a freely rotatable manner by the dynamic pressure bearing sleeve. A bottom end surface at the center part of the rotary hub opposes in close proximity a top end surface of the dynamic pressure bearing sleeve, thereby forming a thrust dynamic pressure bearing section.
A lubricating fluid is filled in the thrust dynamic pressure bearing section, and dynamic pressure generating grooves in herringbone shape, for example, are concavely formed as a dynamic pressure generating means for the lubricating fluid, such that the pressurizing effect of the dynamic pressure generating grooves generates dynamic pressure in the lubricating fluid.
A fluid sealing section is formed on the outer side than and adjacent to the thrust dynamic pressure bearing section, which is made of a capillary sealing section and serves to prevent the lubricating fluid inside the thrust dynamic pressure bearing section from flowing outside. The fluid sealing section is formed by taking advantage of the outer circumference surface of the dynamic pressure bearing sleeve, for example, and is formed between the outer circumference surface of the dynamic pressure bearing sleeve and the inner circumference surface of a circular ring-shaped member mounted on the rotary hub.
A magnetic disk that is rotated by the dynamic pressure bearing motor is made of aluminum alloy, glass or resin. The material of the hub on which the magnetic disk is mounted and which rotates in a unitary fashion with the magnetic disk is selected to have a thermal expansion coefficient virtually equivalent to that of the magnetic disk material. This is to prevent the disk from warping as a result of temperature changes. Normally, aluminum alloy hubs are used with aluminum alloy disks, and ferrite stainless steel hubs are used with glass disks.
In general, aluminum alloy disks are cheaper than glass disks. However, an aluminum alloy hub that fits to an aluminum alloy disk is relatively soft and the mechanical strength obtained when the hub is joined with a rotary shaft is not sufficient; this consequently requires some structural ingenuity. To enhance the mechanical strength, a motor may be equipped with a hard coupling member that is placed between the inner circumference side of an aluminum alloy hub and the outer circumference side of a rotary shaft such that the hub and the rotary shaft are joined in a unitary structure.
As described above, when forming a thrust bearing section by utilizing a top end surface of a dynamic pressure bearing sleeve, a circular ring-shaped member that serves as a fallout stopper member is positioned to project out to the position of a holder member that holds a stator core; this inevitably causes the holder member to be shortened by that much in the axial direction. This results in a shorter joining length between the holder member and the stator core, which causes the holding strength of the stator core to be reduced, which in turn leads to larger electromagnetic vibration of the stator core.
Furthermore, since the joining length in the axial direction of the circular ring-shaped member would also be insufficient, the joining strength of the circular ring-shaped member would lend to be insufficient; and dust from adhesive in a joining section of the circular ring-shaped member could enter a sealing section positioned in the vicinity of the circular ring-shaped member and cause contamination.
In the meantime, a motor apparatus may be designed such that a holder member""s length in the axial direction is lengthened to match that of a stator core. However, by doing so, a circular ring-shaped member that serves as a fallout stopper member for a rotary hub cannot be mounted because of the holder member, and this leaves no choice but to provide the fallout stopper member parallel in the axial direction to a radial bearing section. This causes the radial bearing section""s span in the axial direction to be shortened and the bearing rigidity to decline, and the motor""s height in the axial direction would have to be lengthened in order to obtain sufficient bearing rigidity for the radial bearing section.
In conventional dynamic pressure bearing motors, copper alloys such as phosphor bronze or iron alloys such as ferrite stainless steel are used as the material for a sleeve that serves as a dynamic pressure bearing member. When using an aluminum alloy disk, it is preferable to use aluminum alloy also as the material for a rotary hub. However, using aluminum alloy as the material for the rotary hub that makes up a thrust bearing does not provide sufficient hardness; consequently, the rotary hub that makes up the thrust bearing comes into contact with an end surface of a sleeve, which serves as a dynamic pressure bearing member, whenever there is a start or stop operation, which causes the rotary hub to wear quickly and the dynamic pressure bearing to have a short life.
The present invention relates to a dynamic pressure bearing motor in which a fallout stopper member for a rotary hub can be firmly fixed in a space-saving manner, using a simple structure.
The present invention also relates to a dynamic pressure bearing motor in which the wear on a rotary hub can be controlled and the service life of a dynamic pressure bearing extended even when a rotating member made of an aluminum material comes into contact with a dynamic pressure bearing member in start and stop operations.
In accordance with one embodiment of the present invention, a dynamic pressure bearing motor is equipped with a dynamic pressure bearing sleeve for supporting a rotary shaft by a dynamic pressure; a rotary hub coupled to the rotary shaft; a thrust dynamic pressure bearing section formed between the dynamic pressure bearing sleeve and the rotary hub; and a circular ring-shaped member that is placed to surround an outer circumference surface of the dynamic pressure bearing sleeve, and has a hub mounting section joined to an end surface of the rotary hub in a region radially outside of the thrust dynamic pressure bearing section and a main body section that inwardly protrudes from the hub mounting section. A fluid scaling section that prevents a lubricating fluid inside the thrust dynamic pressure bearing section from flowing outside is formed between the hub mounting section and an outer circumference surface of the dynamic pressure bearing sleeve, wherein the fluid sealing section is defined by a gap in the radial direction formed continuously from the thrust dynamic pressure bearing section. The dynamic pressure bearing sleeve includes a fallout stopper flange section that protrudes outward in the radial direction and opposes in the axial direction the main body section of the circular ring-shaped member to prevent the circular ring-shaped member from falling out in the axial direction. The inner circumference surface of the hub mounting section is positioned to oppose in the radial direction the outer circumference surface of the fallout stopper flange section of the dynamic pressure bearing sleeve.
According to the dynamic pressure bearing motor having such a structure, due to the fact that the hub mounting section of the circular ring-shaped member is positioned on the outer circumference side of the fallout stopper flange section provided on the dynamic pressure bearing sleeve, the hub mounting section of the circular ring-shaped member does not spatially interfere with a holder member that extends in the axial direction to hold a stator core. As a result, the height in the axial direction of a stator core holding section of the holder member can be extended to reach the hub mounting section of the circular ring-shaped member. As a result, the stator core is joined to the holder member with a sufficient joining force, which favorably controls the magnetic vibration of the stator core.
Especially by forming the height in the axial direction of the stator core holding section of the holder member to be equivalent to the height in the axial direction of the stator core held by the holder member in the dynamic pressure bearing motor, the joining force of the stator core can be obtained sufficiently and as required.
In one aspect of the present embodiment, the rotary hub may be provided with a fixing section that protrudes in the axial direction from an end surface in the axial direction of the rotary hub, which fixes the hub mounting section of the circular ring-shaped member through plastic deformation. The inner circumference surface of the fixing section may be formed as a regulating surface that positions the hub mounting section of the circular ring-shaped member. As a result, the hub mounting section can be readily mounted on the rotary hub with high precision due to the positioning regulating surface of the fixing section; and this results in a firmly fixed state between the hub mounting section and the rotary hub through the plastic deformation of the fixing section.
The dynamic pressure bearing motor may be further provided with a circumferential wall section that collects a coating sealer for the plastically deformed fixing section formed on the rotary hub outer side in the radial direction of the fixing section. As a result, contamination that may be caused by plastically deforming the fixing section can be favorably prevented and the lubricating fluid can be favorably prevented from flowing outside the fixing section by the coating sealer.
In the dynamic pressure bearing motor, the fluid sealing section may have a capillary sealing structure whose gap dimension gradually enlarges towards an opening of the fluid sealing section, and both of the outer circumference surface of the dynamic pressure bearing sleeve and the inner circumference surface of the main body section of the circular ring-shaped member, which together form the fluid sealing section, may have a tapered surface that slopes inward in the radial direction towards the opening of the fluid sealing section, such that the center axial line of the fluid sealing section slopes inward in the radial direction towards the opening. As a result, the centrifugal force during rotation, in addition to the inherent capillary sealing effect of the fluid sealing section, works to push inward the lubricating fluid inside the fluid sealing section, which results in an substantially favorable sealing effect.
In accordance with another embodiment of the present invention, a dynamic pressure bearing motor is equipped with a dynamic pressure bearing member for supporting a rotary shaft by dynamic pressure; a rotary member that rotates with the rotary shaft in a unitary fashion; a thrust dynamic pressure bearing section formed between the dynamic pressure bearing member and the rotary member; and a circular ring-shaped member having a mounting section that surrounds an outer circumference surface of the dynamic pressure bearing member and a main body section that protrudes radially inward from the mounting section, wherein the mounting section is joined to an end surface of the rotary member in a region radially outer side of the thrust dynamic pressure bearing section. The dynamic pressure bearing member includes a fallout stopper flange section that protrudes outward in the radial direction and opposes in the axial direction the main body section of the circular ring-shaped member. The main body section of the circular ring-shaped member overlaps the fallout stopper flange section to prevent the dynamic pressure bearing member from falling out in the axial direction.
The inner circumference surface of the mounting section of the circular ring-shaped member is positioned to oppose on the outer side in the radial direction the outer circumference surface of the fallout stopper flange section of the dynamic pressure bearing member. The dynamic pressure bearing motor also includes a stator core holding section that is provided to oppose in the axial direction the mounting section of the circular ring-shaped member and oppose in the radial direction the main body section of the circular ring-shaped section.
As a result, the length of a holder member that holds a stator core can be sufficiently extended in the axial direction, and the height in the axial direction of the stator core holding section of the holder member can be extended to a position in the vicinity of the hub mounting section of the circular ring-shaped member. This results in sufficient joining force for the stator core and in a favorable control of the magnetic vibration of the stator core.
In accordance with another embodiment of the present invention, a dynamic pressure bearing motor is equipped with a rotating member that is rotatively driven in a unitary fashion with a rotary shaft; a dynamic pressure bearing member that rotatively supports the rotary shaft by dynamic pressure; and a thrust dynamic pressure bearing provided in a region where an end surface in the axial direction of the dynamic pressure bearing member and an end surface in the axial direction of the rotating member oppose each other in the axial direction. The rotating member includes a rotary hub that is made of an aluminum material and has a disk mounting section, and a thrust plate that is provided on the rotary hub and is made of an iron material and makes up a part of the thrust dynamic pressure bearing. As a result, wear on the rotary hub is controlled and the life of the dynamic pressure bearing can be extended, even when the hub and the dynamic pressure bearing member come into contact in start and stop operations.
In one aspect of the present invention, the dynamic pressure bearing member may have an expanded diameter section, in which the diameter of an end section in the axial direction of the dynamic pressure bearing is expanded outward in the radial direction, and the thrust dynamic pressure bearing section can be formed in a region where the end surface on the expanded diameter section side of the dynamic pressure bearing member and the thrust plate oppose each other in the axial direction.
In another aspect of the present invention, the expanded diameter section of the dynamic pressure bearing member may preferably be interposed between the circular ring-shaped member and the rotating member, in order to prevent the dynamic pressure bearing member from falling out the rotating member, and vice versa.
In another aspect of the present invention, the circular ring-shaped member may preferably be positioned in the axial direction by abutting itself against the thrust plate provided on the rotating member. By having the circular ring-shaped member abut against the thrust plate, the gap at the thrust dynamic pressure bearing section in the thrust direction stabilizes and the fluctuation in the dynamic pressure force in the thrust direction can be reduced.
In another aspect of the present invention, the rotary shaft can be fitted in a unitary fashion on the inner circumference side of the thrust plate and the rotating member can be mounted in a unitary fashion on the outer circumference side of the thrust plate. With such a structure, the bonding strength between the hub made of an aluminum material and the rotary shaft can be increased.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.